Fuel cells, particularly acid fuel cells, are comprised of an anode chamber, an anode electrode on a substrate, an electrolyte matrix, a cathode electrode on a substrate, a cathode chamber, an electrolyte reservoir plate, and a separator plate. These components are aligned electrically in series such that a stack of fuel cells can be employed in the production of electricity.
The electrolyte reservoir plate is a porous structure filled with electrolyte. During fuel cell operation, the electrolyte reservoir plate supplies electrolyte to the fuel cell to replenish electrolyte which has been lost by evaporation therefrom. Due to the constraints of the electrolyte reservoir plate formation process, these plates are costly to manufacture and possess limited strength.
For example, electrolyte reservoir plates can be formed in a dry-laid process where graphite powder, powdered phenolic resin, and fibers are showered onto a slow-moving belt to form a layer. The layer enters an oven where it is compacted with a second belt to form a 0.150 inch thick layer which is heated until the phenolic resin melts and coats the graphite powder and fibers. The resin is then cured, thereby bonding the graphite powder and fibers in a composite. Although this is a common electrolyte reservoir plate formation process, the forming speed is slow and it is difficult to incorporate relatively long fibers which are necessary for electrolyte reservoir plate structural integrity- Longer fibers tend to become entangled in the dry-laid feeder, thereby forming fiber bundles in the finished composite. This fiber bundling, which corresponds to uneven fiber distribution, creates weak areas within the composite which are susceptible to structural failure. Composite structural integrity is maximized at fiber lengths greater than about 1.0 mm (about 0.040 inches) while the dry-laid process is limited to fiber lengths of about 0.51 mm (about 0.02 inches).
An additional disadvantage of the dry-laid process is the post formation impregnation of two parallel edges of the composite with a substance such as hydrophilic ink to form a gaseous edge seal when filled with electrolyte. This prevents a possible mixing of fuel and oxidant utilized in the fuel cell. The impregnation, however, becomes increasingly difficult if the electrolyte reservoir plate thickness increases above about 0.10 inches, if the density increases to about 1.0 g/cc or greater, if the median pore diameter decreases to below about 20 microns, and/or if any of these parameters are not substantially uniform throughout the composite. Consequently, the tolerances in the specification for the electrolyte reservoir plate are small and the fabrication is difficult, resulting in many rejected parts.
What is needed in the art is an improved electrolyte reservoir plate which is more efficient to process, and has improved structural integrity and gas edge barriers.